A commonly known type of a driving circuit employs a peaking tecnique for driving, at a high speed, a light emitting element (e.g., an LED) whose response speed is relatively slow. See, for example, Japanese Pat. No. 2844682. With the peaking technique, an instantaneous current (hereinafter referred to as a “peaking current”) is given to a light emitting element so as to force the light emitting element to respond at a high speed. FIG. 21 shows an exemplary configuration of a common conventional light emitting element driving circuit using a peaking technique. FIG. 22 shows waveform diagrams illustrating an operation of the conventional light emitting element driving circuit shown in FIG. 21.
The conventional light emitting element driving circuit shown in FIG. 21 includes a light emitting element 101, a peaking current generating section 102, and a light emitting element driving section 103. A digital signal S (the waveform (a) of FIG. 22) is inputted to the light emitting element driving section 103. The peaking current generating section 102 generates a spire-shaped peaking current P (the waveform (b) of FIG. 22) at the rising and falling edges of the digital signal S. The light emitting element driving section 103 receives the digital signal S and the peaking current P, and outputs a driving current D (the waveform (c) of FIG. 22) whose waveform is obtained by combining together an amplitude current according to the amplitude of the digital signal S and the peaking current P. The light emitting element 101 receives the driving current D, and outputs an optical signal (the waveform (d) of FIG. 22) whose waveform substantially matches that of the digital signal S. This is how it is possible to realize a high speed response of the light emitting element 101.
However, the response speed that can be realized with the conventional light emitting element driving circuit described above is on the order of Mbps at best. Realizing a response speed on the order of 100 Mbps or more requires the use of a very large peaking current P, which causes a problem that the reliability of the light emitting element 101 is lowered over a long-term operation, or the like.